1. Field of the Invention
The invention relates to a process and equipment for the neutralization and precipitation of acidic or acidcontaining pollutants in flue gases of furnaces, especially from incinerating plants, with utilization of the heat from the furnace.
2. Description of the Prior Art
In order to neutralize acidic or acid-containing pollutants in flue gases of furnaces, the conventional methods involve using neutralizing agents, for example, aqueous suspensions of lime, which are sprayed continuously into the flue gases by means of pump-driven liquid atomizers. By this process, the pollutants are transformed into neutral salts while the carrier solution which is introduced with the suspension is dried at the same time. The neutral salts, together with the flue dust are then removed from the flue gas in a dust separator.
In such processes, the neutralization has been carried out at flue gas temperatures higher than 500.degree. C., so that considering the temperature limit imposed by the dew point, a cooling span of about 350.degree. K. is available. This large cooling span permits the introduction of a relatively large amount of liquid in the form of a suspension of very low viscosity. This is advantageous with respect to obtaining a fine dispersion in the flue gas which, in turn, aids the chemical reaction.
If, however, flue gases are supplied from plants which utilize the waste heat, the flue gas temperatures are only about 200.degree. to 250.degree. C. and therefore, a cooling span of only about 100.degree. K. is available for this process. If the furnace is an incinerator in which heterogeneous fuel is processed, great fluctuations in both the amount of flue gas produced and the concentration of pollutants occur. In order to ensure the desired reduction in pollutants even at high concentrations of pollutants, the neutralizing agent is in each case metered out in amounts corresponding to the highest amouht and concentration of flue gas. This naturally requires a high consumption of neutralizing agent. On the other hand, the amount of water, introduced in the case of such an inflexible system is based on the smallest amount of flue gas production which occurs.